(1) Autogenous nitrogen-fixing bacteria refer to various free-living prokaryotes that can independently fix atmospheric nitrogen, including many physiological types, such as nitrogen-fixing bacteria, Klebsiella, Clostridium pasteureum, etc. Photoautotrophic and aerobic Nostoc commune, photoheterotrophic facultative anaerobic Rhodotorula, photoautotrophic facultative anaerobic chromobacter, etc.

⑵ * * Nitrogen-fixing bacteria: refers to a prokaryotic microorganism that can only fix nitrogen when symbiotic with other organisms. Include rhizobia, Frankliniella, Anabaena and lichen, which have nodules with leguminous plants.

⑶ Combined nitrogen-fixing bacteria: refers to prokaryotes that must live in plant rhizosphere, leaf surface or animal intestine to fix nitrogen. Include Azospirillum, which can fix nitrogen in the rhizosphere of tropical plants, and Beijerinckia. All nitrogen-fixing bacteria have nitrogenase, which can fix nitrogen in strict anaerobic microenvironment protected by oxygen barrier. Biological nitrogen fixation is extremely important for the existence, prosperity and development of the global biosphere, and also plays an extremely important role in human survival and agricultural production increase.